Coupler



FIG. 1 is a front perspective view of a coupler comprising our design;

FIG. 2 is a lateral view of a coupler;

FIG. 3 is a rear view of a coupler;

FIG. 4 is a lateral view of a coupler;

FIG. 5 is an elevated perspective view of a coupler; and,

FIG. 6 is a lateral perspective view of a coupler.

The broken lines depict portions of the article that form no part of the claim. 

CLAIM The ornamental design for a coupler, as shown and described. 